1. Technical Field
The present invention relates to the field of spin-valve sensors.
2. Background Art
Data is stored on magnetic media by writing on the magnetic media using a write head. Magnetic media may be formed in any number of ways, such as tape, diskette, hard disk, or the like. Writing involves storing a data bit by utilizing magnetic flux to set the magnetic moment of a particular area on the magnetic media. The state of the magnetic moment is later read, using a read head, to retrieve the stored information.
Data density is determined by the amount of data stored on an area of magnetic media and depends on how much area must be allocated to each bit. To decrease bit size, head size is decreased by fabricating thin film read and write heads. Thin film heads commonly employ separate write and read heads.
One type read head employs a spin valve sensor. Spin valve sensors exploit changes in electrical resistance which occur as a result of manipulating the relative orientation of the magnetization of ferromagnetic layers within the spin valve sensor.
In conventional spin valve sensors, one ferromagnetic layer has its magnetization pinned while another, which has its magnetization set perpendicular to the pinned player, is free to change its magnetic orientation in response to magnetized bits on adjacent recording media. Thus, the magnetized bits on the recording media change the relative magnetization between the pinned layer and the free layer so that the sensor presents a high resistance state when the magnetizations are antiparallel and a low resistance state when the magnetizations are parallel. An induced current through the spin valve is used to detect changes in the resistance of the spin valve that results from changes in the relative magnetizations of the pinned and free layers.
As data bits are made smaller to increase data density, the magnetic field generated by the smaller bits becomes weaker. As such, there is less magnetic field to rotate the free layer. As a result, the free layer must be made thinner so it can respond to the weaker magnetic fields.
One result of reducing the thickness of the free layer, however, is that it also reduces the performance of the spin valve. Reducing the thickness of the free layer decreases the giant magnetoresistance of the spin valve. As the thickness of the free layer becomes ever smaller, the giant magnetoresistance decreases more significantly. In addition, decreasing the thickness of the free layer can also increase the magnetic hardness and the sheet resistance of the spin valve. Thus, in conventional spin valves, spin valve performance, and ultimately data density, is limited by free layer thickness.